1. Field of the Invention
This invention relates to a method for producing cigarettes containing at least two different tobacco mixtures.
2. Description of the Related Art
It is well known that the use of a single tobacco mixture for producing cigarettes can lead to certain drawbacks in that, for example, in a cigarette that tobacco portion furthest from the lit end behaves as a filter during cigarette combustion, and retains the combustion products to give the final part of the cigarette a taste which gradually differs from that of the initial part.
In order to adjust the aforesaid characteristics at will, it has been proposed to manufacture cigarettes using several tobacco mixtures located in different cigarette zones so that the said characteristics become influenced in a required and determined manner during the cigarette combustion time.
To obtain cigarettes of this type, manufacturing machines have been proposed having a suction belt conveyor to which two tobacco layers of different types are fed in succession and disposed one on the other by two ascending shafts. Pneumatic means are associated with a portion of the suction conveyor which communicates with the first shaft in order to periodically inhibit deposite of tobacco of the first type, so that on said conveyor portion there forms a first discontinuous tobacco layer, of which those zones free from tobacco are then filled with tobacco of the second type by the second shaft. Trimmer means disposed downstream of the second shaft along the path of said conveyor then make the thickness of the overall tobacco layer obtained uniform.
It has however been found that manufacturing machines of the aforesaid type are not able to produce cigarettes which are exactly equal to each other, ie containing constant proportions of the two tobacco mixtures, this being attributable to the fact that because of the fibrosity of the treated tobacco the said pneumatic means are not able to precisely and uniformly define the tobacco-free zones of the first layer, which therefore have dimensional differences which influence the cigarette characteristics.
Another type of manufacturing machine able to produce cigarettes of the described type is known, in which two ascending shafts disposed one following the other successively feed a suction belt conveyor with two continuous layers of tobacco of different types.
At the outlet of the first shaft, a trimmer device removes equidistant tobacco portions from the first layer to create spaces which are then filled with tobacco of the second type by the second shaft. A second trimmer device disposed downstream of the second shaft along the path of said conveyor then makes the thickness of the overall tobacco layer obtained uniform. A drawback of manufacturing machines of this type is that the two said trimmer devices trim away a large quantity of tobacco, which is known to result in considerable quality loss.